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BULETINUL INSTITUTULUI POLITEHNIC DIN IAŞI
Publicat de
Universitatea Tehnică „Gheorghe Asachi” din Iaşi
Tomul LVI (LX), Fasc. 2, 2010
SecŃia
TEXTILE. PIELĂRIE
THE PROPERTIES OF KNITTED FABRICS FOR
BIO-FUNCTIONAL TEXTILES
BY
ELENA ONOFREI
Abstract. “Bio-active” textiles belong to the so-called “Functional” textiles that in
addition to their basic functions claim to take care of the health and hygiene of the
consumer contributing to his well-being.
Fabric characteristics are usually dictated by a specified end-use. Understanding the
relationship between the fabric end-use and fabric properties becomes fundamental
for classification, selection, and proper utilization of apparel fabrics. This study focused
on the effect of knitted structures on SeaCell active/Lycra yarn knitted fabric properties.
In this work, we have used three structures: single jersey, single piqué and double piqué,
for production of the knitted fabrics.
Key words: bio-active fibres, knitted fabric structure, thermal properties, air
permeability, water vapour permeability.
1. Introduction
Customer desire for comfort, hygiene and well-being has created a large
and rapidly increasing market for “Bio-active” textiles. “Bio-active” textiles
belong to the so-called “Functional” textiles that in addition to their basic
functions claim to take care of the health and hygiene of the consumer
contributing to his well-being. These products use biocides as the active agents.
Some biocides are applied at the finishing stage while in other cases the
biocides can be incorporated into synthetic fibres during extrusion. The
obtained products vary in their effectiveness and durability depending on the
type of fabric, the biocide and the finishing method used [1].
Estimations have shown that the production of “Bio-active” textiles was
in the magnitude of 30,000 tones in Western Europe and 100,000 tones
worldwide in 2000. In 2005 “Bio-active” textile production was almost 175,000
tones and it was estimated that the production increased by more than 15% a
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year in Western Europe in the next period, will making it one of the fastest
growing sectors of the textile market [2].
In fact, the term “Bio-active” textiles cover the following products:
• Anti-bacterial textiles - products aim at reducing the proliferation of
bacteria, including those responsible for microbial odours;
• Anti-dust mite textiles - products aim at eliminating the waste products
of dust mite responsible for bronchial and asthmatic allergies;
• Anti-fungal textiles covering foot fungus (e.g. athlete's foot), black
mildew in bathrooms, fungal contamination of mattresses and bed linen and
products reducing mould and fungus in carpets and floor coverings. In practice,
anti-fungal textiles generally provide anti-bacterial and/or anti-dustmite
properties as well, so that these products can be included either under antibacterial or anti-dust mite properties, according to the main effect targeted [3].
Anti-bacterial textiles account for more than 70%, versus less than 30%
for anti-dust mite textiles.
The main negative factor limiting the potential growth of “Bio-active”
textiles is that the most biocides used on commercial textiles can induce
bacterial resistance to these substances, which can lead to increased resistance
to certain antibiotics in clinical use. Bacterial resistance may be a particular
concern because large quantities of biocides are needed on the textiles to
achieve adequate activity and durability [2].
An antimicrobial textile can act in two distinct ways:
− By contact: The antimicrobial agent placed on the fibre does not disperse
and, to attain the antimicrobial action, micro organisms have to contact the fibre.
− By diffusion: The antimicrobial agent placed on the surface or in the
fibre disperses more or less rapidly in a humid external medium to reach the
micro organisms and inhibit their growth.
SEACELL® is a multifunctional cellulose fibre with bio-active
properties. Seaweed is added as the active substance to protect the skin and have
anti-inflammatory properties. The structure of Seacell® facilitates the active
exchange of substances between the fibre and the skin – nutrients such as
calcium, magnesium and vitamin E are released by the natural body moisture
when the fibre is worn, thereby creating a complete sense of well-being [4]. The
“active” version with added silver is for extra antimicrobial properties. 6,900
mg/kg silver ion in fibre, make the fibre hold forever antibiotic characteristic
[5]. Trials with bacterial and fungal cultures at the University Hospital of Jena
have established that the active fibre has antimicrobial properties. In addition to
the antibacterial activity, tests were conducted to also evidence the antimycotic
and fungicidal effect of SeaCell® active. The antimicrobial effect – while at the
same time maintaining the typical skin-friendliness of cellulose fibres in
SeaCell® active – was examined and confirmed by numerous tests, including
those conducted at the Hohenstein research institute [4]. The bactericidal effect
of silver ions on micro-organisms is very well known, but the bactericidal
mechanism is only partially understood. It has been proposed that ionic silver
Bul. Inst. Polit. Iaşi, t. LVI (LX), f. 2, 2010
77
strongly interacts with thiol groups of vital enzymes and inactivates them [6], [7].
2. Experiments
The goal of the research was to study changes in the properties of
knitted fabrics as a function of their structure. In this study, we changed only the
knit structure of the samples, in order to isolate the effects of other variables.
2.1. Materials
The yarns used for knitting the fabrics were 20 SeaCell® pure/10 SeaCell®
active/70 Combed Cotton, Ne 50 and Lycra 70D. Adding Lycra to a fabric gives it
stretch and recovery and these properties are important particularly in active
sportswear and outdoor activities where body flexing and stretching occur. Also,
Lycra supports muscles, delaying fatigue and extending the endurance.
No.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
Table 1
Yarn Characteristics: SeaCell
Parameters
Unit of measure
Linear density, Ttex
g/km
CV of yarn count
%
Twist
Tpm
CV of Twist
%
Uster Irregularity
%
Thin places/1000 m of yarn
Num
Thick places/1000 m of yarn
Num
Neps/1000 m of yarn
Num
Tenacity
cN/tex
CV of Tenacity
%
Breaking Elongation
%
CV of Breaking Elongation
%
Average value
11.93
1.246
1284
3.66
13.9
105
456
367
10.15
11.13
3.849
12.97
No.
1.
2.
3.
4.
5.
Table 2
Yarn Characteristics: Lycra
Parameters
Unit of measure
Linear density, Tden
g/9km
Tenacity
cN/tex
CV of Tenacity
%
Breaking Elongation
%
CV of Breaking Elongation
%
Average value
70
16.85
8.41
526
11.7
The USTER Irregularity and Imperfections were determined using the
Uster Tester 3. The Tensile Properties were determined using a HOUNSFIELD
Tensile Tester and twist of the yarn with the Twisttronic Mesdan.
Single jersey and its derivative fabrics Single Piqué and Doppel Piqué
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were selected for this study, since they are widely used.
The fabrics have been produced on the 8-feed Single-Jersey Circular
Knitting Machine MERZ – MBS. The details of machine: gauge – 28 E,
diameter – 13”, speed – 50 rpm, number of needles – 1152. The loop length for
all the fabrics was the same (2.5 mm).
2.2. The Properties of Knitted Fabrics
All tests were carried out after the samples were conditioned in
standard atmospheric conditions (temperature 20 ± 2°C, 65 ± 2% relative
humidity), according to the standard ISO 139:1973 – Textiles - Standard
atmospheres for conditioning and testing.
Table 3
The Properties of the Fabrics
Single
jersey
Thickness, [mm]
1.16
CV of the thickness , [%]
2.93
Fabric weight, [g/m2]
301.80
Fabric density, [g/cm3]
0.260
Air permeability, [mm/s]
850.9
Thermal conductivity,
51.76
(W/mK) x 10-3, (CV %)
(2.26%)
Thermal resistance,
22.48
(m2K/W) x103, (CV %)
(3.76%)
Thermal absorptiveness,
142.2
W s1/2/m2 K, (CV %)
(3.67%)
Water vapour transmission
30.406
rate, [g/m2/h]
Index of water vapour transmission
99.8
rate, [%]
Single
piqué
1.29
3.55
318.98
0.247
821.97
50.74
(2.7%)
25.42
(3.16)
138.36
(2.25%)
Doppel
piqué
1.36
1.5
330.56
0.243
781.97
49.86
(2.07%)
27.27
(2.22%)
134.8
(3.0%)
29.90
29.73
98.19
97.63
The thickness of the fabric depends on the yarn count, knitted structure
and relative closeness of the loops. The fabrics thickness was determined with
SDL – Digital Thickness Gauge M034A, according to the standard EN ISO
5084. From Table 3, it can be seen that the thickness was higher for the double
piqué fabrics and reduced for single piqué and single jersey, respectively. The
tuck-knit combination fabrics showed higher thickness than that of plain knit
fabric, because of tuck stitch accumulation.
Fabric weight per unit area. The double piqué fabrics showed a higher
weight per unit area value and it reduced with single piqué and single jersey,
respectively. So, it can be concluded that the knit-tuck combination showed a
higher weight per unit area value than plain knit fabrics.
The density of the tuck-knit structures is slightly reduced compared
with the single jersey fabric.
Bul. Inst. Polit. Iaşi, t. LVI (LX), f. 2, 2010
79
Fabric Comfort Properties. Clothing comfort is an extremely complex
phenomenon resulting from the interaction of various physical and non-physical
stimuli on a person wearing given clothing under given environmental
conditions. One of the basic variables that have a great influence on comfort is
fabric construction. A lot of thermo-physiological comfort properties, such as
air permeability, thermal resistance, water vapour permeability, water
absorbency and so on, can be altered by fabric construction.
a) Air Permeability. The air permeability of the fabric depends on the
shape and value of the pores and the inter-thread channels, which are dependent
on the structural parameters of the fabric. The effects of knit structures with
spandex on the air permeability of fabric have been analyzed by Çeken [8].
The air permeability of the samples was measured according to standard
ISO 9237 with a Textest FX-3300 air permeability tester. The air permeability
measurements of the fabrics were carried out 10 times, and the average and
standard deviation of the test values were calculated.
Fig. 1 − The air permeability of the fabrics.
As we can see from Fig. 1, single jersey fabric showed the highest air
permeability and double piqué fabric showed the lowest air permeability. In
between these came single piqué fabric. This evolution is determined by reduced
thickness and weight of the single jersey fabric compared with piqué fabrics.
According to the literature the tuck stitch can be employed to produce
openwork effects on knitted fabrics [9] but, because of the stretched structure of
the Lycra yarn the openwork effects is reduced and that determines a more
compact and closer structure.
b) Thermal properties. The thermal properties of the samples are
presented in Table 3. The thermal properties of the fabrics were measured by
the ALAMBETA instrument according to standard ISO EN 31092-1994. The
measurements were repeated 5 times on randomly chosen parts of the fabrics, and
average values were calculated. The coefficients of variation of all properties are
also indicated. The measuring head temperature of the ALAMBETA is
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approximately 32°C, and the contact pressure is 200 Pa in all cases.
Thermal conductivity, λ, [W/mK], is considered to be dominant in
determining the heat transfer through fabrics and garments.
The single jersey structure has higher thermal conductivity. This
situation can be explained by the amount of entrapped air in the fabric structure.
The amount of fibre in the unit area increases and the amount of air layer
decreases as the fabric density increases. As it is known, thermal conductivity
values of the fibres are higher than the thermal conductivity of entrapped air [10].
So, fabrics that contain less still air have higher thermal conductivity values.
Fig. 2 − Thermal conductivity.
Thermal absorptiveness, b, [Ws1/2/Km2], is the heat flow q, [W/m2]
which passes between the human skin and the contacting textile fabric.
Fig. 3 − Thermal absorptiveness.
Bul. Inst. Polit. Iaşi, t. LVI (LX), f. 2, 2010
81
Thermal absorptiveness is the objective measurement of the warm-cool
feeling of fabrics. When a human touches a garment that has a different
temperature than the skin, heat exchange occurs between the hand and the
fabric. If the thermal absorptiveness of clothing is high, it gives a cooler feeling
at first contact [11]. The surface character of the fabric greatly influences this
sensation. A rough fabric surface reduces the area of contact appreciably, and a
smoother surface increases the area of contact and the heat flow, thereby
creating a cooler feeling [10].
The single jersey structure has a smoother surface compares with single
piqué and double piqué structures as can be seen from Figs. 4 and 5. As
consequence, the single jersey structure presents a higher thermal absorptiveness.
So the tuck-knit structure is recommended for a warmer filling at the
contact with the skin and the plain single jersey structure must be preferred for a
cooler feeling.
Single Jersey
Single Piqué
Doppel Piqué
Fig. 4 − Aspect of the knitted structures – technical face.
Single Jersey
Single Piqué
Doppel Piqué
Fig. 5 − Aspect of knitted structures – technical back.
Thermal resistance, r, [m2K/W], mainly depends on thickness and air
porosity nature in the fabric. Double piqué fabric had a higher thermal
resistance than the others due to its higher thickness. It then decreased from
single piqué and single jersey, respectively. Fabrics from tuck-knit combination
stitches showed higher thermal resistance than the fabrics from plain stitches.
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Fig. 6 − Thermal resistance.
c) Water vapour permeability. The ability of clothing ensembles to
transport water vapour is an important factor of physiological comfort. The
water vapour permeability was determined using a SDL Shirley Water Vapour
Permeability Tester M – 261, according the standard BS 7209-1990.
The cup method is a very common method for testing the moisture
transfer ability of fabrics. It is used to measure the rate of water vapour
transmission perpendicularly through a known area of a fabric to a controlled
atmosphere. In this method, a sample covers a cup containing distilled water
and placed in a controlled environment of 20ºC and 65% relative humidity. By
adjusting the initial weight of water in the cup to 46 ml, a constant air gap was
set between the water surface and the sample. The tests lasted for 16 h and the
weight of each cup was recorded initially and after 16 h. The water vapour
transmission rate (WVTR) was calculated by the following equation:
(1)
WVTR =
G
, [g/m2/h]
tA
where: G is weight change of the cup with fabric sample, [g]; t − the time
during which G occurred, [h]; A − the testing area, [m2].
The index of water vapour transmission rate was calculated by the
following equation:
(2)
I=
WVTR
× 100 , [%]
WVTRr
where: WVTRr is the water vapour transmission rate of the reference fabric.
The index of water vapour transmission rate of the single jersey
structure is slightly higher than for the other structures. The existence of this
Bul. Inst. Polit. Iaşi, t. LVI (LX), f. 2, 2010
83
difference is most probably a consequence of the thinner structure of single
jersey fabrics. The transportation of water vapour through a thin fabric will be easier.
3. Conclusions
In order to achieve the ideal clothing comfort, it is necessary to consider
the end-use of the garment when selecting the fabric. According to the results
knit-tuck structures, due to their high thermal resistance values, could be
preferred for winter garments in order to protect from cold and for a warmer
feeling at first contact.
On the other hand, single jersey structures should be chosen for active
sports or summer garments for better moisture management properties, air
permeability and for a higher thermal absorptiveness, that gives a cooler feeling
at first contact with the skin.
A c k n o w l e d g m e n t s. This work was conducted under support of the
FCT - FUNDAÇÃO PARA A CIÊNCIA E A TECNOLOGIA, within the framework of
„Compromisso com a Ciência” initiative of recruiting post doctoral researches into the
national scientific and technological system and the 2C2T - O Centro de Ciência e
Tecnologia Têxtil, Universidade do Minho, Portugal.
Received: September 11, 2009
“Gheorghe Asachi” Technical University of Iaşi,
Department of Technology and Design
of Textile Products
e-mail: eonofrei@tex.tuiasi.ro
REFERENCES
*
* *
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Textiles. Textile Research Journal, 78, 60 (2008).
*
3. * * Bio-Active Textiles. Western Europe (2001 - 2005), © 2004 D&K Consulting S.A.
4. www.seacell.com
5. http://www.ftc.com.tw/prod_bodytek_seacell01e.htm
6. Matsumura Y., Applied and Environmental Microbiology. 69, 4278–81 (2003).
7. Gupta A., Maynes M., Silver S. – Applied and Environmental Microbiology. 64
5042–5 (1998).
8. Çeken F., An Investigation About Air Permeability of Wool/Polyester and
Wool/Acrylic Knitted Fabrics. Tekstil ve Konfeksiyon, 2, 111−115 (1997).
9. David J. Spencer, Knitting Technology. Second Edition, Woodhead Publishing
Limitid, Cambridge England (1996).
10. Frydrych I., Dziworska G., Bilska J., Comparative Analysis of the Thermal
Insulation Properties of Fabrics Made of Natural and Man-Made Cellulose
Fibres. Fibres&Textiles in Eastern Europe, October-December, 40 (2002).
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1.
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Elena Onofrei
PROPRIETĂłILE STRUCTURILOR TRICOTATE CU DESTINAłIE
ARTICOLE BIO-FUNCłIONALE
(Rezumat)
CerinŃele consumatorilor pentru comfort şi igienă au determinat o rapidă
dezvoltare a pieŃii de textile „bio-active”. Textilele „bio-active” aparŃin aşa numitelor
textile „funcŃionale” care, în plus faŃă de funcŃia lor de bază, contribuie la menŃinerea
sănătăŃii şi igienei consumatorului, completând sentimentul de confort. Caracteristicile
produselor textile sunt impuse, în general, de destinaŃia acestora. InŃelegerea relaŃiei
dintre destinaŃia şi proprietăŃile textilelor este fundamentală pentru clasificarea, selecŃia
şi utilizarea corectă a acestora. În lucrare s-a studiat efectul structurii tricoturilor asupra
proprietăŃilor tricoturilor din bătătură, realizate din fire bio-active SeaCell şi Lycra. S-au
utilizat trei structuri diferite: glat, piqué si doppel piqué pentru realizarea tricoturilor.